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  • Author or Editor: M. Wei x
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Abstract  

Characterization of autocatalytic decomposition reactions is important for the safe handling and storage of energetic materials. Isothermal differential scanning calorimetry (DSC) has been widely used to detect autocatalytic decomposition of energetic materials. However, isothermal DSC tests are time consuming and the choice of experimental temperature is crucial. This paper shows that an automatic pressure tracking calorimeter (APTAC) can be a reliable and efficient screening tool for the identification of autocatalytic decomposition behavior of energetic materials. Hydroxylamine nitrate (HAN) is an important member of the hydroxylamine family. High concentrations of HAN are used as liquid propellants, and low concentrations of HAN are used primarily in the nuclear industry for decontamination of equipment. Because of its instability and autocatalytic decomposition behavior, HAN has been involved in several incidents. This paper presents calorimetric measurements for the thermal decomposition of 24 mass% HAN/water. APTAC heat-wait-search and heat-soak-search modes are used to characterize the thermal decomposition of HAN. By comparing the kinetic analysis for the two modes, it is concluded that HAN shows strong autocatalytic decomposition behavior. The most likely decomposition pathway of HAN is proposed to explain the observed autocatalytic behavior.

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To separate minor actinides from HLLW by extraction chromatography, a few novel silica-based di(2-ethylhexyl)phosphoric acid (HDEHP), 4,4¢,(5¢)-di(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6), octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO), and N,N,N¢,N¢-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) polymeric adsorption materials (HDEHP/SiO2-P, DtBuCH18C6/SiO2-P, CMPO/SiO2-P, and TODGA/SiO2-P) were synthesized by impregnating HDEHP, DtBuCH18C6, CMPO, and TODGA into the pores of porous SiO2-P particles, which were the new kind of inorganic/organic composites consisted of macroporous SiO2 and copolymer. The bleeding behavior of these composites was investigated by examining the effect of contact time and HNO3 concentration. It was found that in the tested HNO3 concentration range, a noticeable quantity of DtBuCH18C6, at least 600 ppm, leaked out from DtBuCH18C6/SiO2-P because of the protonation of DtBuCH18C6 with hydrogen ion, while the others were lower and basically equivalent to the solubility of HDEHP, CMPO, or TODGA in corresponding acidities solutions. Based on the batch experiment, the bleeding of CMPO/SiO2-P and TODGA/SiO2-P, the main adsorbents used in MAREC process for HLLW partitioning, was evaluated by column operation in 0.01M HNO3 and 3M HNO3. The quantity of CMPO leaked was ~48 ppm in 0.01M HNO3 and ~37 ppm in 3.0M HNO3. The bleeding of TODGA decreased from 23.2 ppm to 7.27 ppm at the initial stage and then basically kept constant. An actual bleeding of TODGA was evaluated by the separation of Sr(II) from a 2.0M HNO3 solution containing 5.0 . 10-3M of 6 typically simulated elements.

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Summary  

The Minor Actinides Recovery from HLW by Extraction Chromatography (MAREC) process was used mainly for the separation of minor actinides (MAs) and some specific fission products (FPs) from highly active liquid waste (HLW) by the composite CMPO/SiO2-P of the macroporous silica based polymeric octyl(phenyl)-N,N-diisobutylcarbamoylmethylphoshine oxide (CMPO) and others. In this study a cascade of chromatographic separation was performed on a 3.0M HNO3 solution containing 5.0 . 10-3M of 13 elements, at 323 K. The cascade consisted of three columns the first and second ones were packed with CMPO/SiO2-P and the third with SiO2-P particles. The first column was employed to prepare various eluents containing saturated CMPO. The second column was used for separation into groups. The CMPO of CMPO/SiO2-P was recovered from the effluent by the third column and a CMPO-free effluent containing minor actinides was obtained. The elements contained in the simulated HLW of 3.0M HNO3 were separated into (1) a non-adsorption group (Sr, Cs, and Ru etc.), (2) a MA-hRE (heavy rare earth)-Mo-Zr group, and (3) a lRE (light rare earth) group by eluting with 3.0M HNO3, 0.05M DTPA (diethylenetriaminepentaacetic acid) (pH 2.0) and HNO3 (pH 3.5), respectively. The resultant MA-hRE-Mo-Zr mixture containing minor actinides was then separated into the groups (1) Pd-Ru, (2) MA-hRE, and (3) Mo-Zr by utilizing 3.0M HNO3, distilled water, and 0.05M DTPA (pH 2.0) as eluents. More than 92% of CMPO in the MA-hRE containing effluent was adsorbed by SiO2-P particles. The effectivity and technical feasibility of MAREC process were demonstrated.

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Abstract  

A new type of silica-based chelating extraction resin, DtBuCH18C6/SiO2-P, was prepared by impregnating a crown ether derivative, 4,4,(5)-di(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6), into the porous silica/polymer composite particles (SiO2-P). The adsorption of Sr(II) and some other fission product elements was investigated by a batch adsorption experiment in HNO3 medium. It was found that Sr(II) exhibits a strong adsorption onto the extraction resin, while the other fission product elements show almost no or only weak adsorption. The adsorption kinetics of Sr(II) was explained by assuming as the rate-controlling step the complex-formation reaction between Sr(II) and DtBuCH18C6 contained in the extraction resin. The rate equation of Sr(II) adsorption was determined as:-d[Sr(II)]/dt = k[Sr(II)][DtBuCH18C6][NO3 ]0.5.

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Abstract  

Sequestration of radioactive nickel (63Ni2+) in fly ash coming from hospital wastes incineration plant by incorporating nano-goethite as a function of pH, particle size and the ratio of solid and liquid was investigated under the batch leaching experiments. The synthetic nanogoethite was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and specific surface area (SSA). The admired needle nanogoethite was obtained in terms of XRD, TEM and SSA analysis. Approximate 5% of 63Ni2+ was desorbed from the nanogoethite/fly ash composite under the circum natural pH conditions. The ratio of solid to liquid has little effect on desorption of 63Ni2+ from nanogoethite/fly ash composite. These results indicate that the radioactive nickel in fly ash can be sequestrated by incorporating nanogoethite. The results may play significantly a role in immobilization in situ of trace radionuclides in the natural environment.

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Abstract  

Supramolecular 2,3- and 2,5-pyridinedicarboxylate (PDC) intercalated ZnAl-layered double hydroxides (2,3- and 2,5-PDC–ZnAl–LDHs) have been prepared by ion exchange method. The structure and composition of the intercalated materials have been studied by X-ray diffraction (XRD) and inductively coupled plasma emission spectroscopy (ICP). The study indicates that the 2,3-PDC and 2,5-PDC anions are accommodated as interdigitated bilayer and monolayer arrangement respectively between the sheets of LDHs. Furthermore, their thermal decomposition processes were studied by the use of in situ high temperature X-ray diffraction (HT-XRD), and the combined technique of thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS) under N2 atmosphere. Based on the comparison study on the temperatures of both decarboxylation and complete decomposition of interlayer PDC, it can be concluded that 2,5-PDC–ZnAl–LDHs has higher thermal stability than that of 2,3-PDC–ZnAl–LDHs.

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Abstract  

Electroreduction of Tc(VII) was studied in nitric acid solution using glassy carbon electrode. The electroreduction was conducted at a constant potential –300 mV (vs. Ag/AgCl) with a potentiostat. It was found that the difference of the Tc concentration in the solutions before and after the electrolysis was negligibly small. This means that there were almost no TcO2 or Tc deposited on the carbon fiber electrode during the electroreduction. Absorption spectra and distribution coefficients obtained by ion-exchange analysis indicated that Tc(VII) was reduced to Tc(IV).

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Abstract  

Electrochemical reduction of U(VI) in nitric acid-hydrazine solution is greatly influenced by the concentration of nitric acid. In low acidity nitric acid solution such as 0.1M (M=mol/dm3) HNO3, U(VI) was firstly reduced to U(V) and then partially reduced to U(IV). In high acidity nitric acid solution, e.g., 3-6M HNO3, an electrode process of two-electron transfer was involved in the reduction of U(VI). A higher U(IV) yield could be achieved in nitric acid solution with higher concentration. Hydrazine was very effective in suppressing the reduction of concentrated nitric acid, and the optimal concentration of hydrazine added was 0.075 to 0.15M in 6M HNO3

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Abstract  

For in vivo measurement of DNA synthesis in the patient"s tumour 3"-[18F]fluoro-3"-deoxythymidine (FLT) has been shown to be very promising. As a new labeling precursor 5"-O-(4,4"-dimethoxytrityl)-2,3"-anhydrothymidine (DMTThy) was chosen and an organic synthesis was developed including NMR and MS data for characterisation. The 18F-labeling of DMTThy can be performed within 30 minutes in radiochemical yields of almost 20% when using polar solvents such as DMF or DMSO and a temperature of 160 °C. Hydrolysis is completed with 1N HCl at 50 °C within 10 minutes without losses.

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Planar electrochromatography (PEC) is a mode of planar chromatography in which the mobile phase is driven by electroosmotic flow. The variables that affect the performance of PEC with an aqueous mobile phase on a bonded octadecylsilyl layer are discussed. These include the magnitude of the applied electric field, the concentration of the buffer salt, the pH of the mobile phase, and the concentration of acetonitrile used as the organic modifier. The effect of changing each of these variables is illustrated by model separations of a mixture of four compounds of diverse structure.

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